Spark plug construction



May 14, 1946. A. F. MITTERMAIER SPARK PLUG CONSTRUCTION Filed Jan. 22,- 1945 Inventor! 7 Armin F1 Mibterrhaie by ya /6.2M

His Attorney.

between a conductor and Patented May 14, 1946 UNITED @PATENT OFFICE SPARK PLUG CONSTRUCTION Armin F. Mittermaler, Fort Wayne, Ind., asslgnor to General Electric Company,

New York a corporation of Application January 22, 1943, Serial No. 473,155

, 1 Claim.

Referring to the drawing, in Fig. l I have illustrated my invention as applied to an electric ignition device such as a spark plug but it is to be which is electromagnetically coupled with a high voltage winding, not shown, the high voltage being connected to a high voltage electrode H. at the base of the plug. A conventional low voltage electrode. I4 is provided which is grounded through the casing I0. One end of the low voltage winding connects through a conductor l5 which passes through'my improved bushing construction is which will bedescribed below.

The conductor in turn nector [1 to a conductor I8 which forms a part of the harness of the ignition system. Such ignition systems which employ a step-up transformer allow the large percentage of the distribution sysis described and claimed in Patent 2,299,750 Hull tem including the conductor l8 to have a relaet al., and which is assigned to the same assignee tively low voltage so that the system is designed as this present invention. for relatively high altitudes or low pressure opera- It is an object of my invention to provide an tion. In order to maintain the pressure at the deimproved spark plug construction with a bushing sired amount inside the barrel 10 there is prowhich will minimize the possibility of breakage 2o vided an improved spark plug including a sealed when a relatively high pressure exists between the construction with bushing l6 which will withinside and the outside surfaces of the seal. stand relatively high pressure differentials so that- Another object of my invention is to provide a the plug is suitable for high altitudes. Other debushing seal construction between a conductor tails of the ignition system are more completely and a casing of an electric apparatus which will described and claimed in a copending application be simple in construction, easy to manufacture, Serial No. 466,608'Harkness and Robinson, filed and which will withstand a very large pressure November 23, 1942, and assigned to the same asdifferential between opposite sides. signee as this present invention.

Further objects and advantages of m invention In order to provide a spar p u con uct o will become apparent from the following descripwhich will be substantially gas-tight and which tion referring to the accompanying drawing, and will seal a relatively large pressure differential the features of novelty which characterize my inwithout the danger of cracking o t S I D vention will be pointed out with particularity in vide a bushing construction including a body of the claim annexed to and'forming a part of this suitable ceramic material 20, such as glass or specification. porcelain, havin a tube 2| for accommodating This assembly is then heated until upon cooling the gl ss will with a'tube II and band a.

It is customary to make a glass metal seal by embedding an end or a metallic member into the glass. However, I have found that a higher pressure may be sealed by my improved construction including a relatively large portion of cooperating flat surfaces which form the seal between the glass and metal. The metallic member 23 also includes a portion 24 which is bent to form a springlike portion so the metallic member forms a resilient connection between the ceramic material and the support. It will be seen that in Figs. 1 and 2 that the portions 23 and 24 are so formed that the metallic member has a U-shaped cross section. The member 24 is provided with a. shoulder 2! which. as will be seen in Fig. 1, cooperates with an end of the barrel III for supporting the bushing construction. A relatively tight seal between the shoulder 23 and the cooperating surface of the barrel I is formed by relatively tightly forcing members 26 and 21 against the end of the barrel member l0 through a nut member 23. Also, the shoulder 25 may be attached to the supportin: member l0 in any other suitable manner, such as by brazing, as will be described below in relation to Fig. 4. I have found that when my improved bushing is attached to a support it will withstand a pressure difierential or at least about 600 pounds per square inch without breaking the seal between a band 23 which has about onefourth of an inch in height and is sealed to the adjacent surface of the glass bushing. Also, the bushing has been heated from room temperature to 200 F. without damage.

In Fig. 3 I have illustrated another arrangement for obtaining a flexible connection between a body 30 of suitable ceramic material by providing a metallic member having a portion or band 3| with a relatively large surface sealed to the ceramic portion and a second portion 32 which is bent to provide a springlike portion. A shoulder 33 is provided so that the bushing may be relatively solidly attached to a support.

In Fig. 4 I have illustrated a method of assembling my improved spark plug by attaching my improved bushin construction as is illustrated in 2 to the end of the barrel member ID. A small ring shape member 35 of suitable soldering or brazing material is placed between the shoulder 25 and the end of the barrel member I0 and the member 38 may be heated in any suitable memher so as to melt and attach the shoulder 25 to the end of the barrel member ID. A convenient way of forming the brazed connection is to provide a coil 36 around the metallic members which may conduct a high frequency current so as to suitably heat the metallic member by electromag- 2,4oo,sea

netic conduction. However, when so attaching my improved bushing to a support, it is desirable to prevent the current from being induced into the band portion 23 which may cause sufllcient heating to break the seal between the band 23 and the adjacent surface of the ceramic 20. Since the metallic members 24 and 25 have a corrugation or a U-shape it will be seen that a tubular member 31 may be placed between the members 23 and 24 so as to suitably screen the member 23 and prevent current from being induced in the member by the coil 36 during-the brazing operation. Furthermore the metallic member, since it rests on the bottom oi the corrugation, will'help to absorb any heat which tends to how from the portion 24 to the portion 23.

In view oi! the above, it will be seen that I have provided a spark plug particularly suitable for high altitudes and including a bushing construction which is strain-tree, which may withstand differences in expansion characteristics due to temperature of the supporting member ID and the metallic member 24, which provides a minimum height in an axial direction, and which also due to its corrugated construction allows the insertion of a metallic shield for preventing currents from being induced into the band member 23 while the seal is being made between the shoulder 25 and the end of the barrel member i0.

Although I have shown and described particular embodiments of my invention, I do not desire to be limited to the particular embodiments described, and I intend in the app nded claim to cover all modifications which do not depart from the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent 01 the United States is:

In a spark plug for internal combustion engine ignition systems which are adapted for high altitude operation, an elongated generally cylindrical metal casing having a high tension spark gap at one end and a low tension terminal at the other end, a voltage step-up transformer in said casing connected to said low tension terminal, means for both insulating said 10w tension terminal and sealing said transformer against low pressure high altitude operating conditions comprising an annular ceramic insulating member surrounding the said low tension terminal and fused thereto, an annular axially resilient shock absorbing supporting member surrounding said ceramic member and fused thereto, and air-tight means for fastening the outside of said supporting member to the walls of said casing.

ARMIN F. MITTERMAIER. 

